The present invention relates to an electric-field-inducible deformable material which can be fired into a porcelain. More particularly, it relates to an electric-field-inducible deformable material which is fired into a piezoelectric element for an actuator and a sensor which are integrated as an electromechanical transducer for positioning a precise machine tool, control of the optical path length of an optical apparatus, a valve for controlling the flow rate, an ultrasonic motor or an automobile brake apparatus.
The present invention further relates to an electric-field-inducible deformable material which is suitably used as a micro-sensor in an element for measuring the physical properties of liquid, and in an element for measuring very small masses, or in a micro-actuator.
As a piezoelectric material utilized for an actuator, a filter and various sensors, there have hitherto been known Pb(Zr, Ti)O3 (hereinafter referred to as PZT), BaTiO3 and the like. Among them, a PZT system is mainly used since it has better overall piezoelectric properties. In this respect, the Pb contained in PZT system is stabilized and, therefore, does not originally pose a problem of decomposition and the like. However, in some cases, a material containing no Pb is desired depending upon the use. Further, when a Pb-containing compound such as PZT, PLZT and the like is fired at en elevated temperature, a slight amount of Pb is generally vaporized. Therefore, there is a problem that the properties are difficult to be stabilized due to the change in the composition at firing particularly in thin film or thick film uses. On the contrary, although BaTiO3 dose not contain Pb and, therefore, is a candidate material for such the use, since it has inferior piezoelectric properties as compared with PZT system, it has been used as an actuator or a sensor in few cases. Accordingly, for example, JP-A 11-60334 discloses a piezoelectric porcelain composition in which BaTiO3 is used as an actuator. In the composition, the piezoelectric properties are improved by adjusting the composition to enhance the piezoelectric constant.
However, in the aforementioned piezoelectric porcelain composition disclosed in JP-A 11-60334, even an electric-field-inducible deformable material in which the content of Cu is adjusted to 0.05 to 2.0 parts by weight in terms of CuO, relative to 100 parts by weight of a main component, by substituting a part of Ti of BaTiO3 with Zr, can not afford the desired displacement amount for an actuator. In addition, in the resulting piezoelectric porcelain, a crystal phase in which a majority of Cu is dissolved in a perovskite crystal phase expressed as Bax(Ti1-yZry)O3 is formed, but even a composition having a peak piezoelectric constant can not afford sufficient displacement for a piezoelectric material.
Accordingly, the present inventors paid attention to the fact that only the electric-field-inducible deformation, and not the piezoelectric constant, contributes to the displacement properties of a piezoelectric material. It was found that the electric-field-inducible deformation is increased by including Mn, Cu and Co in BaTiO3 and rendering a crystal phase in a porcelain into a single perovskite phase, which resulted in the completion of the present invention. That is, the present invention is an electric-field-inducible deformable material comprising as a main component BaTiO3 with added 0.05 to 2 wt % of at least one selected from Mn, Cu and Co in terms of a metal, wherein a crystal phase in a porcelain is a single perovskite phase and the value of the transversal electric-field-inducible deformation is 300xc3x9710xe2x88x926 or more in the field strength of 2000 V/mm.
Thereby, an amount of a rotating 90xc2x0 domain becomes larger and it is presumed that the electric-field-inducible deformation due to this is increased and, thus, the sufficient displacement amount is obtained as a piezoelectric material.